The present invention relates to client-server communication.
A JavaServer Pages™ (“JSP”)”) page is a markup language page, typically an HTML (Hypertext Markup Language) web page, that contains additional bits of code that execute application logic to generate dynamic content. The application logic may involve various kinds of objects that can be accessed from a JSP page. For example, a JSP page may contain HTML code that displays static text and graphics, as well as a method call to an object that accesses a database; when the page is displayed in a user's browser, it will contain both the static HTML content and dynamic information retrieved from the database. Thus, a JSP page looks like an HTML (or XML) page—it contains text encapsulated by tags, which are defined between angle brackets (“< >”). While HTML tags are processed by a user's web browser to display the page, JSP tags are used by the web server to generate dynamic content.
A JSP page is an example of a dynamic web page, which in this specification will be referred to simply as a server page or a page. There are other technologies, similar to JSP, that can be used to create HTML or XML pages dynamically on a server. These include, by way of example, SAP Business Server Pages (BSP), Microsoft Active Server Pages (ASP), and AOLserver Dynamic Pages (ADP) technologies. In these technologies, functionality is embedded in structure in the form of special tags in a markup language document, and content and structure (presentation) are merged when the page is generated by a server. In alternative technologies for creating server pages, e.g., traditional servlet and CGI (Common Gateway Interface) script technologies, structure and presentation are embedded within functionality to create dynamic web pages.
In this specification, it is sometimes necessary to distinguish the page as it exists on the server from the page as it exists on the client. The term “page document” will be used to refer to the page that is processed by a server—e.g., a .jsp page. The term “browser document” will be used to refer to the page that is received and processed by a client and generally displayed to a human user—e.g., an HTML page generated by processing of a .jsp page by a JSP engine.
A server page can include information for a graphical user interface (“GUI”) to generate a browser document. The server can transmit the browser document to a client through a network. At the client, the browser document is rendered for display. This is typically done by a web browser, such as the Microsoft® Internet Explorer. When a user interacts with the client through the GUI to refresh the page, the entire process is repeated: the whole page, including layout information and data, is generated on the server and the resulting browser document is transmitted from the server to the client through the network. If the network has insufficient bandwidth, transmitting the whole page can cause undesired effects: until the refreshed page is finally presented, there can be a long waiting time or screen flicker.
Some browsers, such as the Microsoft Internet Explorer 6.0, include a feature for flicker-free rendering. When the client receives a modified page, the browser identifies modified components of the page and only replaces these components instead of the whole page, for example, by dynamic HTML injection into the page's Document Object Model (DOM). Dynamic HTML injection can reduce screen flicker for the user, but, because the whole page is transmitted through the network, insufficient network bandwidth can still cause undesirable waiting times.